DEPARTMENT OF COMMERCE 

BUREAU OF FISHERIES 

HUGH M. SMITH. Commissioner 



FISH ISINGLASS AND GLUE 



By George F. White 



APPENDIX IV TO THE REPORT OF THE U. S. COMMISSIONER 
OF FISHERIES FOR I9I7 




Bureau of Fisheries Document No. 852 



PRICii, 5 CENTS 

Sold only by the Superintendent of Docxtments, Government Printing Office 
Washington, D. C. 



WASHINGTON 

GOVERNMENT PRINTING OFFICE 

1917 



A 



AJonograph 



v\\ 










<, 






D. Of D. 
SEP 6 1917 



'X 



FISH ISINGLASS AND GLUE. 



By Geoege F. White. 



COLLAGEN AND GELATIN. 

Collagen, the mother substance of gelatin, is an albuminoid which 
occurs to a large extent in vertebrates and also in the flesh of cepha- 
lopocls. It is the chief constituent of the white fibrils of connective 
tissue and is also found in bones, cartilages, ligaments, fish scales, etc. 
CoUagens of different origins are not of identical composition ; how- 
ever, all show the characteristic albuminoid property of being in- 
soluble in water and the ordinary protein solvents. 

The most interesting and commercially important property of 
collagen is its power to be converted into gelatin by heating with 
water alone or in the presence of dilute acids. On the other hand, 
if gelatin is heated to 130° C. it is transformed back into collagen, 
so that there is a very intimate relation between the two substances. 
For practical purposes we may consider gelatin to be collagen which 
has been converted into a soluble form by combination with water. 
(Other changes have been noted, such as the evolution of ammonia, 
when collagen is treated with water.) The following table gives the 
composition of collagen, gelatins from various sources, and of fish 
glue, which is a crude form of gelatin: 

Composition of Collagen and Gelatin. 





Carbon. 


Nitrogen. 


Hydro- 
gen. 


Sulphur. 


Oxygen. 


Collaeen 


Per cent. 
50.75 

49.38 
50.11 
50.49 
50.34 


Per cent. 
17.86 

17,97 
17.81 
17.90 
17.76 

17.87 


Per cent. 
6.47 

6.80 
6.56 
6.71 
6.96 


Per cent. 


Per cent. 
24.92 


Gelatin from— 


0.7 

.26 
.57 

.58 

.^70 

.66 


25. 13 


Tendons 


25.26 


Ligament s . . . . 


24.33 






Trachea. . . 




Ear 






Air bladder 


48.69 


17.68 
17.51 

17.68 


6.76 




Fish scales . . ... 


.52 






48.69 


6.76 











a Includes sulphur; separate percentage not noted. 



104738°— 17 



4 FISH ISINGLASS AND GLUE. 

Collagens are to a certain extent differentiated by the ease with 
which they are converted into gelatin. Thus the collagenous car- 
tilage of the trachea is transformed at 100° C. into gelatin, whereas 
ear cartilage requires a temperature of 110° ; the collagen of air 
bladders forms gelatin at room temperatures. In general, the for- 
mation of gelatin takes place most readily with fishes and amphibia, 
more slowly with birds, and very slowly with old animals. The 
presence of salts, for example, of sodium chloride in a concentration 
of 10 per cent retards the transformation. 

Gelatin (French gelatine, Latin gelata, that which is congealed) 
is a colorless, amorphous substance which is transparent when in 
thin sheets. It does not dissolve in cold water, but swells in this 
medium. If treated with warm water, it dissolves to a sticky liquid 
which, if sufficiently concentrated, sets to a jelly on cooling. If 
gelatin is boiled with water for several hours (or simply digested 
with water for two days at a temperature of 37° C), it is converted 
into a nongelatinizing form ; further boiling transforms it into pro- 
teoses, peptones, and finally into acids, among which glycocoll is 
present in a characteristically large amount. This fact should be 
born in mind in a study of the commercial uses of gelatin, since 
prolonged boiling, especially in the presence of acids, changes it 
chemically and physically (the gelatinizing) and correspondingly 
the adhesive power is destroyed. 

As a food, gelatin has little nutritive value, and should not be 
substituted for other proteins of the normal diet since not all of its 
nitrogen is in a form which can be utilized by the organism. 

Gelatin, obtained as described above, should not be confused with 
the products derived from alga? and seaweeds of different varieties, 
especially those of the East Indies, China, and Japan. Thus the 
gelatinizing substances obtained from bird's nests, prized as a deli- 
cacy by the Chinese, and Bengal isinglass, or agar, yield carbohy- 
drates in large amount and have no relation chemically to true 
gelatin. 

FISH SOUNDS. 

"^^-liile the principal supply of gelatin is to-day obtained from the 
refuse of animal bones, hides, and hoofs in the slaughter and pack- 
ing houses, the peculiar properties of the gelatin derived from fish 
sounds, called isinglass in the trade, makes this product of consid- 
erable commercial importance. 

The fish sound (air bladder, or swim bladder) is a hollow sac, con- 
taining gas (oxygen, carbon dioxide, and nitrogen), situated in the 
abdominal cavity below the vertebral column. Its principal func- 
tion is probably mechanical. Since it is compressible, it serves to 
regulate the specific gravity of the fish, enabling the latter to rise 



FISH ISINGLASS AND GLUE. 5 

and sink or to maintain its position at a certain water level. In a 
few fishes it may take on the functions of the lung of higher verte- 
brates and may be considered to be the homolog of that organ. 

The size of the air bladder varies to a great extent, being very 
small in some species, whereas in the sturgeon, hake, catfish, and 
carp it is highly developed. In some fishes the sound is practically 
loose in the abdominal cavity, while in others it clings closely to the 
backbone, the intestines, and the abdominal wall. The sound is 
made up of several tunics of which the inner layer is thin, often with 
a silvery luster, containing crystalline substances, sometimes covered 
with a pavement epithelium. The adjacent layer is thick and with 
a fibrous structure; it is the collagen contained in this layer which 
is the source of commercial isinglass. 

Isinglass (probablv a corruption of tlie Dutch huisenblas, German 
hausenblase, literally sturgeon's bladder) has for centuries been 
manufactured and exported from Russia. Several varieties of the 
sturgeon {Acipenser huso or beluga, A. ruthenus or sterlet, A. sturlo 
or common sturgeon, A. stellatus or starred sturgeon), of catfish 
{Silurus glanis), and of carp {Cyprinus carpio), flourishing in the 
Volga and other rivers, in the Caspian and Black Seas, and in the 
Arctic Ocean, yield the well-known Russian isinglass. 

Russian isinglass is generally brought to the great fair at Nijni 
Xovgorod and from there finds its way, through the agency of Petro- 
grad traders, to London and elsewhere. Other sources of supply 
than Russia are Brazil, Venezuela, the East and West Indies, Penang, 
Bombay, Manila, Nova Scotia, Newfoundland, and the United States. 
Russian isinglass is known in commerce as staple isinglass, and is 
sold as long and short staple, according to size. 

Leaf isinglass (Astrakhan leaf, Saliansky leaf, Samovy leaf, 
etc.) is prepared by soaking the sounds in warm water, whereby dirt 
and mucous membrane are removed. The sounds are then opened 
and dried by exposing the inner membrane to the air; the dried 
sounds may be further treated by pounding and rubbing until the 
outer membrane is detached and separated from' the purer, inner 
layer. Book isinglass is prepared in a similar manner, but the 
sounds are folded and covered with a damp cloth. Trimmings from 
the leaf or book are pressed into cakes or tablets or rolled into rib- 
bons and sold as lower-grade isinglass. The trimmings from the 
sounds and other parts of the fish are often boiled in water until 
the gelatin dissolves and the filtered solution is evaporated to dry- 
ness. There is also cake isinglass, so called from its shape, although 
sometimes it is made in a globular form. 

Long staple and book isinglass are the best varieties, a 2 per cent 
solution in hot water setting to a jelly when cold, and yielding only 
0.05 per cent insoluble matter. Cake isinglass is dark colored and 



6 FISH ISINGLASS AND GLUE. 

of unpleasant odor. A low grade of Russian isinglass, also sold 
under the above names, is manufactured from the peritoneum and 
intestines of the fish. Russian isinglass is imported into the United 
States in varying amounts from year to year. 

Iceland produces an excellent grade of isinglass, which is obtained 
from cod and ling sounds, only a little inferior to the Russian prod- 
uct. Venezuela and Brazil export tongue sounds and lump and pipe 
isinglass which are obtained from Siluridse and other less definitely 
characterized fish. Tongue sounds are oblong, tapering, and pointed 
at one end, of firm consistency, but otherwise poorer than the Russian 
product. From Penang and Bombay are exported tongue sounds 
and also purse sounds, so-called from their shapes and their fringed 
edges. 

The value of the imports of sounds into the United States and 
countries from whence imported, according to the census of 1908 
(Fisheries of the United States, 1908, p. 292), are given in the fol- 
lowing statement : 



Canada $G2, 3G." 

United Kingdom 22. 721 

Venezuela 13, 907 

European Russia 6, 706 



British India $4. 113 

All other countries 3. 863 



Total 113,675 



The production of fish sounds in this country has fallen off in the 
last few years, and the demand being good the value of the imports 
has increased. Norwegian cod sounds have been imported at differ- 
ent times. 

North American isinglass is derived from the sounds of hake, 
cod, and squeteague, hake sounds being the principal source. A few 
years ago over 100 tons of hake sounds were obtained annually on the 
New England coast alone, but the production has fallen off consider- 
ably in recent years. Large amounts are imported from Canada and 
Newfoundland. 

Hake sounds from fish caught in deep waters off the coast of Nova 
Scotia are large and of good quality. One ton of these fish yields 
300 to 500 sounds, weighing from 40 to 50 pounds. Hake sounds 
from shallow waters are smaller and of a lower grade; 1 ton yields 
about 600 sounds, weighing approximately, 30 pounds. Hake sounds 
are easily detached from the backbone in dressing the fish on the 
fishing vessels, and then they are salted in barrels. Before salting 
they may be scraped and washed but these operations are usually 
omitted without much injury to the character of the isinglass manu- 
factured from them. AVhen delivered on shore, the sounds are slit 
open and thoroughly washed and the black outer membrane is 
scraped off. They are then dried in the air with precautions to 
prevent access to moisture, since they readily putref}^ The average 
hake sound yields about 85 per cent gelatin. 



FISH ISINGLASS AND GLUE. 7 

Cod sounds are smaller than those of hake and of poorer quality. 
One ton of fish yields 15 to 20 pounds of sounds. As they are more 
firmly attached to the backbone than are hake sounds, they are cut 
off with part of the backbone, scraped, washed, and salted. They 
are then washed and dried on shore. Cod sounds yield only about 
50 per cent gelatin, so that they are much less valuable than hake 
sounds. 

Sounds of the squeteague, which fish occurs along the Atlantic 
seaboard, are at present only little utilized. One ton of fish yields 
about 20 pounds of sounds, which are of as good quality as cod 
sounds. Over 30 years ago about 15 tons of dried sounds of the 
squeteague were sold annually, but the production since that time 
has dwindled to a negligible amount. 

The production and value of fish sounds in the United States as 
reported in the census of 1908 (Fisheries of the United States, 1908, 
p. 43 ) are presented in the f ollow^ing table : 





Pounds. 


Value. 


Maine . . . . . 


23,000 

20,000 

2,800 

73,000 


$1,000 
900 


Fresh 


Salted 


100 


Massachusetts (fresh) . . .. .. ... 


3 100 






United States 


96,000 

93,000 

2,800 


4 100 


Fresh 


4 000 


Salted 


100 







The sounds of many fresh and salt water fishes are at present un- 
utilized. 

TILEFISH- SOUND TEST. 

The sound of the tilefish {Lopholatilus chamceleonticeps) w'as 
tested b}' the writer to determine the character of its principal con- 
stituent and its possible utility. The sound was cut open and a 
portion treated as follows: After thorough washing with water the 
tissue was allowed to stand under a large excess of 0.1 per cent 
sodium hydroxide solution at room temperature so that mucin, haemo- 
globin decomposition products, etc., might be dissolved. The resi- 
due was thoroughly washed with water and then subjected to the 
action of an active trypsin solution containing 0.2 per cent sodium 
hydroxide for 24 hours, the temperature being maintained at 37.5° 
C, and in the presence of chloroform to prevent putrefaction. The 
tissue was largely unaffected, and after washing with water was 
treated successively with alcohol and ether to remove any lipoids. 
The residue, after drying at 70° C. was creamy white, and thin 
layers were transparent. 

On continued boiling with water, much more quickly by the addi- 
tion of a trace of acid, the treated tissue dissolved and the solution 



8 FISH ISINGLASS AND GLUE. 

set to a jelly on cooling. This fact, combined with its ability to with- 
stand tryptic digestion, indicated the presence of collagen in the 
original tissue, and further tests confirmed this conclusion. 

The collagen was rapidly hydrolyzed by pepsin in hydrochloric 
acid solution. It was found to be insoluble in dilute alkalies and 
acids but swelled in the latter on standing. 

An aqueous solution of the collagen (obtained by boiling with 
water) was tested for gelatin as follows: The solution could not be 
coagulated by boiling, by mineral acids, acetic acid, lead acetate, or 
other metallic salts. It could be precipitated, however, by alcohol, 
picric acid, tannic acid in the presence of sodium chloride, or by 
potassium ferroc^^anide in the presence of acetic acid. It gave a 
blue-violet biuret test, but no Adamkiewicz or xanthoproteic reaction. 
Millon's test gave only a slight precipitate with little color. Tliese 
tests show the presence of gelatin and the absence of other protein 
matter. 

The presence of collagen (rough experiments showed that over 
90 per cent of the nitrogenous matter of the swim bladder is col- 
lagen), and the fact that it maj^ be readily converted into gelatin 
allow the sound of the tilefish to be put to the same use as the sounds 
of the sturgeon, hake, and other fishes. 

MANUFACTURE AND USES OF ISINGLASS. 

Isinglass is manufactured by an exceedingly simple process. The 
industry was initiated in the United States in 1821, at Rockport, 
Mass., cleaned hake sounds being pressed into plates. In 1834 tWe 
procedure was somewhat improved, and the cleaned sounds, softened 
to the desired consistency by soaking in water, were converted into 
ribbon isinglass by being passed between solid rollers. The ribbons 
were then dried. In 1848 the solid rollers were replaced by hollow 
iron rollers, through which cold water could flow, and thus prevent 
the ribbons from softening and sticking to the iron, as they are apt 
to do, especially in Avarm Aveather. In 1873 a scraper was placed 
against the rollers to remove all isinglass adhering to them. The 
ribbons were made to the desired thickness by adjustment of the 
space between the rollers. 

The manufacture of isinglass is best carried on through the cooler 
months on account of the softening and putrefying effect of a slight 
rise in temperature. The sounds received, generally, have been pre- 
viously cleaned, perhaps scraped, de-salted, and air-dried. They 
are usually in a hard and tough condition, so they must be first im- 
mersed in water for several hours. Four to six hours may be re- 
quired for the gelatin to absorb enough water to be sufficiently pliable 
to handle. The sounds ma}^ now be run into a cutting machine pro- 
vided with a roller and a set of knives which chop the sounds into 



U. S. B. F.— Doc. 852. 



Plate I. 




FIG. 1.— DRYING HAKE SOUNDS FOR ISINGLASS MANUFACTURE. 




FIG. 2,— ROLLING HAKE SOUNDS FOR ISINGLASS. 



U. S. B. F.— Doc. 852 



Plate II. 




FIG. 1,— DRYING-ROOM OF ISINGLASS FACTORY. 




FIG. 2.— WOODEN SPOOL FOR ROLLING INTO COILS. 



FISH ISINGLASS AND GLUE. 



9 



small pieces. This material is then further mixed and macerated 
between a set of iron rollers, from which it passes to so-called sheet- 
ing rollers. These are the hollow iron rollers, cooled by water and 
provided with a scraper, as mentioned above. The gelatin is con- 
verted into sheets one-eighth to one-fourth inch thick, 6 to 8 inches 
wide, and of variable length. These sheets are finally passed 
through ribbon rollers until the ribbons produced are one-sixty- 
fourth of an inch thick; the width is the same as that of the sheets. 
The ribbons are dried in a few hours by being suspended in mod- 
erateh^ warm, light rooms; they are then rolled on wooden spools 
into coils weighing less than a pound each. About 20 per cent of 
the weight of the original sounds is lost during their conversion into 
isinglass. 

A product called transparent or refined isinglass is manufactured 
by dissolving New England isinglass in hot water and spreading the 
solution to dry on oiled cloth. Very thin, transparent sheets are 
thus produced, and these yield an excellent grade of glue, but retain 
a rather pronounced fishy odor. 

When the best grades of isinglass are treated with hot water, they 
SAvell uniformly, produce an opalescent jelly, and finally entirely 
dissolve. Isinglass is insoluble in alcohol, but readily soluble in 
most dilute acids and alkalies. Wlien ignited, isinglass should yield 
no more than 0.9 per cent ash, whereas poorer grades of fish glue, 
or gelatin, jdeld from 1.5 to 4 per cent ash. 

Isinglass has been adulterated by rolling a layer of gelatin between 
two layers of isinglass. Such adulteration may be detected by 
treating with water and observing the nature of the colloidal solu- 
tion under the microscope. Isinglass retains its characteristic fibrous 
structure which is not present in a gelatin solution; the gelatin be- 
comes more transparent than before, the shreds being disintegrated. 
Both of these effects would be observed in the adulterated article. 

The results of the analyses of some different forms of isinglass 
are presented in the following table :" 



Source of isinglass. 


Ash. 


Water. 


Residue 

insohible 
in hot 
water. 


1 Source of isinglass. 


Ash. 


Water. 


Residue 

insoluble 

in h t 

water. 


Astrakhan 


Per cent. 
0.20 
.37 
.20 
.SO 
.50 
.40 


Per cent. 
16.0 
18.0 
17.0 
19.0 
19.0 
17.0 


Per cent. 
2.8 

. 7 
1.0 
3.0 

.4 
1.3 




Per cent. 
1..30 
.13 

.60 

.78 

2.30 

• 


Per cent. 
19.0 
19.0 
17.0 
18.0 

17.0 


Per cent. 
2 3 




! Iceland 


5.2 
21 6 




■ East Ind 'a . . 


8 




i Yellow, unkno\\Ti 


15 G 









It may be readily observed that the Eussian isinglass (Astrakhan ^ 
is by far the best of those samples analyzed. 

" ProIIius, I. F. : Abs. Journal of the Chemical Society, p. 647. 1884. London. 



10 FISH ISINGLASS AND GLUE. 

The use of isinglass for edible purposes has become practically 
obsolete since the manufacture of gelatin on a large scale has become 
a function of the slaughter and packing houses. It was formerly 
utilized to stiffen jellies and jams and in the manufacture of con- 
fectionery, but has no peculiar medicinal properties. Some fish 
sounds have been esteemed as an article of food ; thus it is said that 
fried cod sounds have a flavor resembling that of oysters similarly 
cooked. 

Isinglass has long been used as a clarifying agent for beverages 
such as cider, wines, and malt liquors. The peculiar clarifying 
action is purely mechanical, those substances causing turbidity be- 
coming entangled in the slowly sinking network of gelatinous mate- 
rial. This property is not possessed to the same degree by gelatin 
prepared from animal bones, hoofs, or hides, and such gelatin is far 
less efiicient as a clarifier. English brewers of malt liquors prefer 
the Penang product, while Scottish brewers employ Russian leaf 
isinglass. English cider manufacturers generally use Russian long 
staple. American brewers formerly considered Russian isinglass as 
superior to other kinds, but later adopted the use of the ribbon 
isingless made from hake sounds in this country. 

White wines are usually clarified by isinglass. The isinglass is 
allowed to swell in water and then in wine until it is practically 
transparent. It is thoroughly beaten with more wine, a little tartaric 
acid being eventually added ; after filtering through linen it is stirred 
into the wine. One ounce of isinglass will usually clarify 200 to 500 
gallons of wdne in 8 to 10 days. 

In the storage of beer after the primary fermentation all sus- 
pended particles do not settle in the stock tanks. This is true of 
starch granules, bacteria, some of the protein matter, etc. From 
storage the beer is run into chip casks where it is carbonated by 
charging with carbon dioxide directly or by the addition of young 
beer, and at the same time clarified or fined. This latter process is 
carried out by the addition of chips or of isinglass, or by filtration. 
When isinglass is employed, it is treated with sour beer, acetic, or 
other Aveak acid whereby it is not actually dissolved, but is " cut " 
by the acid. Finings thus prepared have an excellent clarifying 
action. One pound of isinglass will fine 100 to 500 barrels of beer. 

Isinglass is the basis of some of the best adhesives. Although 
formerly used for postage stamps, envelopes, and gummed paper, the 
dextrins prepared from starch have largely taken its place. Mixed 
with two parts of alcohol a " diamond " cement is obtained, the 
cooled solution forming a white, opaque, hard solid. Dissolved in 
acetic acid another powerful cement is obtained, especially useful in 
repairing glass, pottery, and similar articles. Various modifications 



PISH ISINGLASS AND GLUE. 11 

of these cements are prepared, particularly by the addition of some 
adhesive gum which will render the cement insoluble in water. Fol- 
lowing is the formula for one of these : 10 grams isinglass, 5 grams 
gum ammoniac, 5 grams mastic, 80 grams alcohol. The isinglass and 
gums are dissolved separately in the alcohol and then heated together 
over boiling water. The excellent properties of isinglass as a glue 
may be illustrated by the fact that leather belts for machinery are 
repaired by the use of this agent. (In the trade it is often called 
Russian fish glue.) 

Court plaster is made with isinglass as the adhesive. The pro- 
portions used are 10 grams isinglass, 40 grams alcohol, 1 gram 
glycerin, and water and tincture of benzoin in sufficient amount. 
The isinglass is dissolved in enough water to make the total weigh 
120 grams. One-half of this solution is spread in successive layers, 
with the aid of a brush, on taffeta stretched on frames; each layer 
is allowed to dry before the next is applied. The second half of the 
isinglass solution is mixed with the alcohol and glycerin, and is 
applied to the cloth in a similar manner. The reverse side of the 
taffeta is covered with a layer of tincture of benzoin and allowed to 
diy. The above quantities are sufficient to cover a piece of taffeta 
38 centimeters square. 

Mixed with a gum, isinglass has been used as a size for textile 
goods, imparting a luster and stiffness to linens and silks. Com- 
bined with water, Spanish liquorice, and finely divided carbon, in- 
dia ink may be made. A patent for waterproofing fabrics has been 
obtained by Van Winkle and Todd (English patent 20G90, 1890), 
who recommend a combination of isinglass and pyroxylin dissolved 
in acetic acid; experience has shown that a bichromate must be 
added to the mixture or the isinglass rendered insoluble by formalde- 
hyde for the mixture to be successfully used. Isinglass has in past 
years been used to adulterate milk, the addition of a small amount 
adding considerably to the body. 

The manufacture of isinglass in this country is rather inconsider- 
able as compared with the supply of fish sounds. According to the 
census of 1908 ("Fisheries of the United States in 1908," p. 282), 
the value of the annual production of isinglass in this country was 
reported to be $150,000, all of this coming from Massachusetts. 

FISH GLUE. 

Glue is gelatin contaminated usually with various decomposition 
products such as gelatoses, peptones, and organic acids. The purer 
the gelatin the better glue it yields, so that a good glue should be as 
free as possible from other proteins, from h^^drolytic splitting prod- 



12 FISH ISINGLASS AND GLUE. 

nets, and from ash. Fish ghie is usually made up into liquid glue, 
for which there is a reasonably large dem.and. The manufacture 
of mucilage and pastes of various sorts from the dextrins obtained 
from starch has largely limited the demand for fish glue so that 
enterprises based solely on this product have not been very profitable^ 

The manufacture of fish glue in this country has been confined 
practically to three States, Massachusetts, Maine, and California, 95 
23er cent of the value of the product being credited to Massachusetts. 
For 1908 the value of the entire output in the United States was 
$631,000; the value of the New England output was $011,000 and of 
the Pacific coast output $20,000. 

In New England fish glue is made from cod heads, skins and bones, 
haddock residues, and all fish offal containing little or no oil, as this 
constituent is fatal to the production of a good glue. The refuse 
from salting factories forms«a very large part of the source of supply, 
as salt codfish is prepared in considerable quantities in this region. 
The refuse from sturgeon and the skins and scales of menhaden and 
herring have been used. Green and Tower '^ have shown that 1 ton 
of menhaden yields 20 pounds of dry scales from which 10^ pounds 
of pure gelatin (containing IG per cent moisture) may be obtained. 
In this connection it may *be noted that the adhesive qualities of the 
" stick " obtained by the present methods of concentrating the waste 
liquors of the menhaden industry are due to the large percentage of 
gelatin present; this material as now manufactured has use only in 
the fertilizer industry, as it contains too much salt, oil, and foreign 
protein- substance to be serviceable for glue. Many 6ther fish residues 
are now unutilized; such is the case of the mullet of the southern 
waters, which yields an excellent quality of glue. 

In the last few j'^ears whale blubber has been utilized for the pro- 
duction of glue. According to the German patent 131315, the blub- 
ber is chopped up, freed from most of the fat by pressing m the cold, 
and the remainder of the fatty matter is extracted by some solvent, 
as benzene. B}^ this method all the fat is recovered and a fat-free 
dry residue consisting of tissue containing the gelatin is obtained, 
and this may be readily converted into glue. 

Attempts to produce glue from the grayfish {Squalus acanthias) 
have not been successful on account of the large amount of oil and 
water in the fish, the difficulties attended with the extraction of the 
oil, and the presence of dark pigments in the skin which discolor the 
extracts. It is also probable that the skeleton contains only a small 
amount (if any) of collagen or glue-forming substance. . The flesh 
of the smooth grayfish {Mustelus canis) contains gelatin-forming 
material and presents possibilities as a source of glue. 

U. S. Fish. Com. Bull., 1001, p. 97-102. 



FISH ISINGLASS AND GLUE. 13 

MANUFACTURE AND USES OF FISH GLUE. 

In the manufacture of fish glue the fish wastes are first washed 
thoroughly with cold water to remove dirt and blood from the fresh 
fish and salt from the salted fish. The washed material is allowed to 
drain, the wasliings being discarded, and then is subjected to the 
action of hot water or steam. 

In the older methods of preparing glue the crude material was 
treated with w^ater and the mixture boiled in open glue kettles for 
several hours until the collagen had all been converted into gelatin 
which dissolved in hot water. This method yields a fairly good 
glue if the raw materials are clean and fresh, but because of the 
lengthy time required for complete extraction the liquor obtained is 
usually dark colored and contains in solution many other protein 
substances than gelatin. Glue thus prepared is often a poor adhesive 
and is malodorous. 

Newer methods of fish-glue manufacture involve heating the stock 
with steam imder pressure in an autoclave so that the extraction pro- 
ceeds rapidly and there is less time for decomposition of the fish 
protein to occur. In some plants the stock is placed in tall iron cyl- 
inders, steam- jacketed, and heated for several hours until the whole 
mass is thoroughly digested. By a better method, the stock is placed 
within the inner, perforated section of a double boiler. Steam enters 
the inner vessel from the outer, and the whole is heated under pres- 
sure. The glue liquor filters out of the inner vessel and may be 
drawn off from the outer jacket continuously. Sometimes an alter- 
nate action of steam and cold water on the stock is brought into play, 
and this process repeated until the extract is too dilute to be profit- 
ably worked up into glue. 

The digested fish wastes may be filter pressed and the residue 
dried. The resulting product, containing 45 to 55 per cent protein 
matter, and 1 to 2 per cent oil, is a valuable by-product ; in fact, on 
account of the demand for it, the scrap can be considered to be the 
main product of the industry and the glue to be of only secondary 
importance. At any rate, the manufacture of glue alone would not 
pay. The better grades of scrap are used for poultry food under the 
name " chum," while second grades are sold for fertilizer, for which 
there is always a good market. 

The solutions running from the autoclaves or the filtrate from the 
filter presses are run into vacuum condensers, since the excess moist- 
ure in the glue liquor must be distilled off at as low a temperature 
as possible in order to prevent unnecessary decomposition of the 
dissolved gelatin. In general, vacuum evaporators consist of a 
spherical or cylindrical iron vessel, steam-jacketed and provided in- 
ternally with steam coils immersed in the glue liquor. Sometimes, 



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14 FISH ISINGLASS AND GLUE. 

in modern plants, a type of evaporator used has revolving steam 
coils; the solutions are thereby uniformly heated and undue frothing 
from local superheating is prevented. The distilling head is pro- 
vided with baffle plates and is connected with a vacuum pump and 
condenser. To conserve fuel, the steam from one evaporator is led 
through the coils and jacket of the next in a series, on the principle 
of multiple effect. After concentration to the desired consistency 
(fish glue contains usually about one-half its weight of water) the 
product (fish glue) is run while still hot through cloth filters into 
a receiving tank. 

Since fish glue generally does not yield a very good jelly when 
cooled, on account of the presence of impurities, it is employed as 
liquid glue. To prevent the glue from gelatinizing at room tempera- 
tures an acid such as hydrochloric or acetic acid is added, and the 
adhesiveness of the material is little affected. Since it is not required 
that thisliquid glue be heated or be applied to hot surfaces, there has 
been a reasonably large demand for it. It has been largely used as 
a size for straw goods, especially where it has been treated with sul- 
phurous acid, since this latter agent bleaches the straw; it is also 
employed as a size for textiles. Good grades of fish glue are used for 
court-plaster, but isinglass is a better adhesive for this purpose. The 
greatest demand for fish glue comes from the general demand for a 
liquid adhesive. 

Davidowsky* describes the manufacture of fish glue as follows: 

The principal point to be observed in tlie manufacture of fisli glue is tbe 
removal of the skin, which is effected by means of dilute sulphuric acid. After 
the removal of the last traces of acid, the fatty matter of the fishes is saponified 
by treatment of milk of lime frequently renewed. After washing out the lime, 
the pulpy mass is placed in a solution of sodium hyposulphite, alum, and sodium 
chloride, and left for a few days. The liquor is drawn oft and replaced by a 
mixture of solutions of alum, dilute sulphuric acid, and nitric acid. After 
macerating in this mixture for a few days, the mass is thoroughly washed and 
boiled to a glue, and the resulting product is clarified with sulphurous acid or 
alum. 

As will be seen, the entire process requires many chemicals, and besides, the 
yield of glue, which has no especially good qualities, is small. It is used as 
a substitute for isinglass for clarifying. 

That the manufacture of fish glue alone is not very profitable may 
be seen from the fact that glue manufacturers do not rely on this one 
product as a source of profit. Thus, one Massachusetts company sells 
large quantities of fertilizer and also cod-liver oil. Another offers to 
the trade glue, ink, lubricating oil, paste, mucilage, and other 
products. 

" Davidowsky, P.. ]00.": " (Jlnc sclntiii. anhiial char-onl, phosphorus, cfinonts, pastes, 
and mutihige." Trauslali'd frojii thi- (Jcniian by W. T. Dranut. I'hiladelphia. 



FISH ISINGLASS AND GLUE. 15 

Lambert ° discusses fish glue and describes its manufacture as 
follows : 

The fish offal is carried by conveyors to a series of washing tanlvs phiced 
overliead, and thoroujihly waslied with water to remove tlie blood, etc. From 
thence it falls by gravitation into the digesters, and is heated with "live" 
steam for 10 hours. The oil and gelatinous water are drawn off by a pipe fixed 
to tlie bottom of each digester, into tanlvs, tlie oil skinnned from the surface, 
and the glue liquors clarified with a small portion of alum. On filtering they 
are concentrated in open vats provided with a steam coil, to a strength of 32 
per cent dry glue, and then bleached with sulpluu-ous acid. Tlie residue in tlie 
digester is converted into guano. 

Fish glue Is a light brown viscous liquid with offensive odor and acrid taste. 
It forms a sticky mucilage when diluted with water, and as met with in com- 
merce, already contains about one-half its weight of water and such liquid is 
weight for weight, only about equal to a dextrine in viscosity. 

Tlie asli of fisli glue is comparatively high, about 4 per cent on body dried 
at 100° C. It is usually wliite in color, and lias besides carbonates of calcium 
and potassium, some 5 to 10 per cent phosphate of calcium. Fish glue is said 
to assume a greenish-yellow color on boiling with potasli and absorbs about 9 
per cent of the caustic. Liquid gums of this class are easily distinguished by 
boiling with Fehling's solution, when they assume a violet color, and by the 
tannic-acid reaction. The best method to remove the unpleasant odor and 
taste of fish glue is to boil the solution in a little water with 1 per cent phos- 
phate of sodium and to add 0.25 per cent of saccharine. 

The offensive odor of fish glue may also be disguised by the addi- 
tion of creosote, oil of sassafras or wintergreen, or other substance 
with a strong odor. 

There ha^•e been several methods proposed for the testing of glue, 
none of wdiich are perfectly satisfactory. Among the more connnon 
tests are those of the viscosity and consistency of the jelly formed. 
The adhesive powder of the glue, how^ever, does not depend on the 
character of the jelly entirely. Glue is sold with regard to its 
physical properties, especially its color; all fatty matter should be 
absent. 

" Lambert, T., 1905 : " Glue, gelatin, and their allied products." London. 

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